How Transmissive Film Works

3M designs and manufactures several different types of transmissive films that can be used alone or combined together within the same product to enhance the performance of the LCD display.

Let's talk about brightness first. 3M uses two different kinds of brightness enhancement films for the LCD displays in the BMW concept car. The first is a single sheet of polymer imprinted with a prismatic surface pattern. The pattern looks like the teeth of a gear or a series of triangles pointing out from the flat film surface.

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The prisms on the brightness enhancement film redirect light from the backlight toward the viewer. Without these prisms, a lot of the light from the backlight would be wasted -- shining too high or too low for the viewer to see. Think of a non-LCD television set whose light reflects off the ceiling and floor. With brightness enhancement film, all of the light is directed straight out toward the viewer, with any excess light reabsorbed by the back panel of the display.

The second transmissive film used to increase brightness is called dual brightness enhancement film. Its name comes from the fact that the film is not only mounted with prisms, but with an extra reflective sheet for recycling any light that doesn't hit the prism at the correct angle. In this configuration, light continues to bounce around the back of the LCD display until it strikes the brightness enhancement film at the optimal angle to be directed out toward the viewer.

Antireflection transmissive films can be applied to the surface of an LCD display to reduce glare and increase clarity. 3M's antireflective film is actually several layers of film in one. The top layer is an antifingerprint film that makes it easy to wipe fingerprints from PDA or computer screens. The second layer is antiglare film, which reflects light at multiple angles, diffusing the glare effect. A third layer protects PDA screen from scratches. And a fourth layer is a nontacky adhesive that allows the film to be easily removed and replaced in case of scratches or other damage [source: 3M].

For privacy and security issues, 3M has developed light control films that use microlouvers to block screen images from anyone who isn't directly in front of the LCD display. Microlouvers are like microscopic Venetian blinds that point straight out toward the viewer. Anyone to the left or the right of the screen will only see black. 3M sells a special product for laptop and other LCD computer monitors called a Privacy Filter. The privacy filter is essentially a light control film that can be adhered directly to a computer screen.

Another type of transmissive film called enhanced specular reflector film can be applied behind the backlight to maximize the distribution of light from of a single light source. The enhanced specular reflector film is actually made up of hundreds of microscopically thin polymer layers of alternating high and low frequency reflectors. The result is a reflection rate of more than 98 percent, greater than the normal silver mirror you have in your bathroom [source: 3M].

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